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What causes cancer?

Cancer Institute NSW

Published 30 October 2018

Most cancers are not caused by a single event. There are usually several different things that happen over time to damage cells or make them divide more, increasing the chance of them becoming abnormal.

Cell mutations can result in cancer

Usually when cells in the body divide, the new cells are exact copies of the old cells. When this process goes wrong, the new cells are slightly different from the old ones.

This change happens in the genetic material (DNA) inside the cells, and is called a mutation.

While most cells with mutations will die or not cause any problems, a very small number will go on to cause cancers.

What makes cells mutate?

The more often cells divide, the greater the chance of mutations occurring.

Most mutations are spontaneous, with no real reason for the change, however there are certain things that can cause mutations or make cells with mutations more likely to become cancers. These include:

damage to cell DNA

radiation, including ultraviolet radiation from the sun

chemicals in tobacco smoke

substances produced by the body, called reactive oxygen species

cells dividing more often

getting older, which increases the number of times cells have divided

the female hormone oestrogen which stimulates some cells in the breast or womb to divide

abnormal cells not dying

the human papilloma virus can help abnormal cells in certain areas of the body to continue to live and divide.

Do you or someone you care about have cancer?

Visit Patient Information to learn about cancer diagnosis, treatment and possible side effects. You will find practical advice about dealing with cancer and finding support.

We also recommend links to more detailed information.

What are cancer risk factors?

Things that increase the chance of getting cancers are called risk factors.

Some risk factors can't be changed, like a person's age or family background. Other risk factors can be changed. These are usually called lifestyle risk factors.

Risk factors for cancer include:

Getting older—many cancers are more common as people get older.

Family history—some families carry a faulty gene that can be passed on from one generation to the next, with family members who carry the gene having an increased risk of certain cancers.

Smoking—lung cancer and several other cancers can be caused by chemicals in tobacco smoke.

Alcohol—excess alcohol use has been linked to a number of different cancers.